1. Field of the Invention
The present invention relates generally to the field of lithography processing. More particularly, the present invention relates to the field of lithography process modeling.
2. Description of Related Art
Lithography process modeling may be used to account for process effects at various stages in manufacturing integrated circuits (ICs), for example, to help produce ICs that more accurately match their intended layout. Process modeling therefore helps increase IC yield and/or allows ICs to be designed with relatively smaller features to help increase performance and reduce power consumption.
Process models may be used to help account for optical proximity effects, phase shifting effects, distortions introduced by resist processes, and/or etching process effects, for example, in performing optical proximity correction (OPC), phase shifting, silicon verification, and/or mask defect prediction, for example. The N-abled™ Process developed by Numerical Technologies, Inc. of San Jose, Calif., for example, enables the generation of such process models.
A process model may be initially generated from various stepper and optical lithography parameters that are to be used in printing a target pattern. To account for optical and/or chemical effects not captured in the initial model, the model may be calibrated based on actual linewidth measurements on wafer of test patterns printed using those parameters. The calibrated model may then be used, for example, to help predict one or more critical dimensions (CDs) for the target pattern in designing, manufacturing, and/or inspecting a mask to print the target pattern.
As one example, a process model may be used to help predict the printed width of a polysilicon line of a target pattern. If the line is to be printed using phase shifting proximate to and on only one side of the line, however, the line will be printed asymmetrically, that is with different edge offsets, relative to the target pattern. Because the model does not account for such asymmetric printing of features and therefore presumes features will be printed symmetrically, that is with substantially the same edge offsets relative to the target pattern, any resulting mask may not print the target pattern with sufficient accuracy because the line will be printed in a position different than that expected from the model.
The performance of OPC on the target pattern using the model may therefore lead to contact misplacement, bridging, and/or a minimum spacing violation, for example. Because such error conditions may not be revealed until a mask is manufactured and either inspected or used to print the target pattern, any resulting mask and the time and resources expended to manufacture and inspect the mask may be wasted unless the mask can be repaired. This is so even if the resulting mask layout is verified against the target pattern by simulating the printing of the mask layout because the simulated printing of the mask layout will be based on the same model.